1. Field of the Invention
The present invention relates to an antenna carrier comprising antenna elements to be connected to an air vehicle, said antenna carrier projecting from a mounting area forwards or rearwards seen in the longitudinal direction of the air vehicle.
2. Description of the Related Art
The development of the radar technique represented by SE 468 184 B produced the need for providing an aircraft with two parallel, elongate carriers of antenna elements. This was originally solved by means of two rearwardly directed soft bags of cloth which were mounted in the tail of the aircraft. Antenna elements in the form of flexible metal strips were fixed along each cloth bag. In flight, the cloth bags were filled with air, thus expanding and assuming the shape of two parallel cylinders. A problem arising in such rearwardly directed antenna carriers is the turbulence that arises behind the aircraft, which in unfavourable circumstances may cause strong vibrations in the antenna carriers. A further problem is the fact that the antenna carriers and the antenna elements are easily damaged in take-off and touchdown. Therefore a solution involving rigid antenna carriers have been found desirable.
An aircraft consists in mechanical terms of an elastic body with critical eigenfrequencies which vary depending on the type of aircraft. A type of aircraft on which it has been desirable to mount the above-mentioned parallel, elongate carriers of antenna elements has, for example, critical eigenfrequencies which are approximately in the range 5-20 Hz, For the antenna carriers to be supported in a stable and safe manner by the aircraft, their eigenfrequencies must be well separated from the critical eigenfrequencies of the aircraft, i.e. the eigenfrequencies of the antenna carrier must be well outside the range in question.
Forwardly and rearwardly directed antennae mounted on aircraft have been known for a long time in different designs. Since they have been relatively short, they could be formed with such high rigidity in antenna and mounting in relation to the length of the antenna that the eigenfrequencies of the antenna can be located above the critical eigenfrequencies of the aircraft. Moreover, in the usual design only one antenna of the forwardly or rearwardly directed type is attached to the aircraft, which allows the antenna to be fixed to a stronger structure such as the nose or tail of the aircraft. The prior-art constructions of forwardly and rearwardly directed antennae on aircraft have not been found suitable for supporting antenna elements in two parallel and relatively long antenna carriers.
The object of the invention is to provide an antenna carrier which allows two parallel, relatively long, forwardly or rearwardly directed antenna carriers to be mounted on an air vehicle and be supported by the same in a stable and safe manner with small relative motions.
A further object is to provide an antenna carrier which is designed in such manner that the eigenfrequencies of the antenna carrier can easily be separated from the critical eigenfrequencies of the air vehicle.
The features of the invention are defined in the claims.